There has been known a technology for mounting an optical element such as a semiconductor laser on a substrate using a solder. For example, there have been known a method of soldering an optical element and a group of electrode pads formed on a substrate at an equal interval using a self-alignment effect generated by surface tension of the solder, and a method of soldering an optical element and a group of metal layers formed on a substrate and having a smaller planar size than the optical element.
In the method in the related art of mounting an optical element on a substrate by soldering using the self-alignment effect, positional precision of the optical element with respect to the substrate may not be sufficiently obtained in some instances. For example, in some instances, a positional deviation of the optical element with respect to the substrate may occur when disturbances such as shaking, vibration, and inclination occur during the soldering of the optical element and the substrate.
The followings are reference documents.    [Document 1] Japanese Laid-Open Patent Publication No. 07-235566 and    [Document 2] Japanese Laid-Open Patent Publication No. 2005-038970.